Studies will be carried out to gain an understanding of the physiologic role of placental thyrotropins in the control of thyroid function during normal and abnormal human pregnancies. Circulating blood levels of human chorionic and pituitary thyrotropin will be measured at serial intervals during normal pregnancy and related to the levels of free and total thyroxine. Content of human chorionic thyrotropin in the individual placentas of these patients will be measured. Human chorionic thyrotropin will be purified by ion exchange chromatography, gel filtration, and affinity chromatography. The thyroid function of patients with hydatidiform mole and choriocarcinoma will be studied and the thyrotropin elaborated by the abnormal trophoblast will be isolated and compared with the thyrotropin extracted from normal placentas.